Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$54.33	8.734%	$59.0752	$59.08	$59.10	$59.10
Purchase #2	$136.47	12.226%	$153.1548	$153.15	$153.15	$153.20
Purchase #3	$214.60	6.356%	$228.24	$228.24	$228.25	$228.20
Purchase #4	$23.39	3.768%	$24.2713	$24.27	$24.25	$24.30
Purchase #5	$215.40	10.641%	$238.3207	$238.32	$238.30	$238.30
Purchase #6	$29.62	10.259%	$32.6587	$32.66	$32.65	$32.70
Purchase #7	$31.49	9.849%	$34.5915	$34.59	$34.60	$34.60
7 purchase totals =	$705.30		$770.3122	$770.31	$770.30	$770.40